Electrical measuring instrument



Nov. 4, 1947. M. 5. WILSON ET AL summon. umsunme INsTnuuENT Filed Au 9,1946 2 Sheets-Sheet l d w Y n n r o 0 M m @W A v h 00 MEW a r F Nov. 4,1947.

M; 5. WILSON ETAL ELECTRICAL MEASURING INSTRUMENT Filed Aug, 9, 1946 2Sheets-Sheet 2 Their Attorney Patented Nov. 4, 1947 ELECTRICAL MEASURINGINSTRUMENT Myron S. Wilson, Lynn, and Francis M.

Maiden, Mala,

assignors to General Electri \Company, a corporation of New YorkApplication August 9, 1946, Serial No. 689,422

9 Claims. (01. 171-45) Our invention reiatu ,to direct current,permanent magnet type, electrical measuring instruments, and its objectis to provide a sensitive long scale measuring instrument in which thematerials are efliciently used and the parts are compactly assembled,with provisions for removing the complete armature assembly as a unitwithout disassembly of the remaining stationary parts of the instrument.The structure is such as to assure a constant reluctance permanentmagnet circuit after initial permanent assembly and polarization of suchcircuit without the use of a keeper.

The features of our invention which are believed to be novel andpatentable will be pointed out in the claims appended hereto. For abetter understanding of our invention, reference is made in thefollowing description to the accompanying drawings in which Fig. 1 is aperspective top view of the armature assembly framework; Fig. 2 i aperspective top view of the permanent magnet and main portion of themagnetic circuit; Fig. 3 represents a small portion of the magneticcircuit structure which is fastened to and is removable with thearmature assembly; Figs. 4 and 5 represent plan and sectional side viewsof the completedinstrument, Fig. 5 being taken on line 55 of Fig. 4, andFig. 6 represents a modified form of integral permanent magnet fieldassembly which is magnetized after assembly and requires no keeper.

Referring now to the drawings, we employ a permanent magnet assembly asbest shown in Fig.2 which is radially magnetized as in United StatesLetters Patent No. 2,272,767 to Corson. The permanent magnet material Iused is of high corrosive force such as described in United StatesLetters Patent No. 1,947,274 or No. 1,968,569 to Ruder. Cast integralwith the inner pole face of the magnet is a tubular soft iron pole shoe2 having a circular inner periphery of approximately 250 degrees arc,defining the outer side of the circular armature air gap. The outer ring2 and i central core I are made in one piece. These parts are preferablymade of magnetic sintered iron and the magnet i is die cast within theinner and outer rings 2 and 2, and hence, these parts are permanentlyand intimately secured together providing a magnetic circuit ofexcellent efilciency. The structure is permanently magnetized after suchassembly. The inner core 4 is divided into two similar nearlysemi-circular parts and symmetrically joined to the outer ring 3 bydivided tongue parts 5, leaving a key shaped opening between them. Whenthe instrument is assembled, the key shaped opening is occupied bycertain portions of the armature assembly to which is fastened a magnetpart 6, Fig. 3, which fits into the gap at I and completes the circularinner core at this point. with the part 6 in place, a circular air gapof about 250 degrees arc length is completely defined by magneticmaterial and across which gap a uniform radially directed flux isforcedby the permanent magnet I. We prefer to use an air gap which is circularanduniform and of a length of inch. It is to be noted that the divisionof the inner core into two symmetrical sections, symmetrically joined tothe outer ring 2 and to the manetic plug 8, assures uniformity in theflux crossing the circular air gap. That is, the division of themagnetic circuit is symmetrical. The reason for the removable plug 8 ito permit the armature coil to be threaded over the core 4 with one sidewithin the core and the other side in the circular air gap.

The armature assembly framework is shown in Fig.1 and comprises a diecasting of nonmagnetic material comprising a top. plate 8 with upperthreaded lugs 9 for mounting the scale plate lil (see Figs. 5 and 6)downwardly extended feet It with bolt openings therethrough for securingthe frame to the .magnet by bolts l2, an upper bracket I3 for mountingthe upper jewel screw it and upper lead-in spiral l5, and a lowerbracket It for mounting the lower iewel screw l1 and lower lead-inspiral I 8. The downwardly extending lower bracket i8 is shaped anddimensioned to fit easily within the key shaped opening in the centralpart of the permanent magnet assembly of Fig. 2 and has a central sectorshaped part is with a dovetailed key face 20 machined thereon which fltsa dovetailed slot 2| in magnetic core part 8. Part 8 is mounted frictiontight on part 20 and hence is removable with the armature assembly.

The armature assembly framework carries the armature coil 22, armatureshaft 23, and pointer 24 as best shown in Fig. 5. The inner ends of thelead-in spirals I5 and I8 are secured to the shaft 23 and the shaft ispivoted in the upper and lower Jewel screws i4 and II. when thearmatureassembly is removed but with the bolt openings therein forsecuring it to the magnet in alignment with the corresponding boltopenings in the magnet assembly part 2 shown at 25. Fig. 2, the shaft 23is centrally aligned with respect to the center of the magneticassembly, and the yoke of the lower bracket i8 is properly aligned withthe portion 28 of the key shaped opening in the magnetic assembly withthe sector shaped part i8 surrounding the shaft 23 and in alignment withone side of the central portion of the key shaped opening, andsupporting magnetic core part 6 in place on keyway2ll and in alignmentwith part 1 of such opening. In inserting the armature assembly in placein the magnet assembly and likewise in withdrawing it, the armature coil22 is first rotated directly over and surrounding plug 6 and hence inalignment with opening I.

a This is the armature position shown in Figs.

4 and 5. The coil is dimensioned relative to the opening at I so thatthe lower coil end can pass through such opening. Hence, as the completearmature assembly is lowered into the magnet assembly, the parts areguided by the shape of their aligned surfaces, and the lower side ofcoil 22 passes down through gap I followed by core part 6 which thuscloses the opening as the armature assembly is lowered into properposition. We prefer to provide a slight taper to the yoke of bracket i6and in the corresponding surface of the portion 26 of the opening in themagnetic assembly such that the bracket and opening are slightly largerat the top than at the bottom. We have used a taper of /2 degree here.The surfaces of parts 8, l9, and i6 and the corresponding surfaces ofthe core parts 4 and 5 where contact is made when the armature assemblyis in place are finished and nicely fitted so that the armature assemblyis rigidly locked in correct position, with the shaft 23 centrallyaligned and with the armature coil22 free to rotate in the circular airgap provided. The outer surface of core part 6 is flush with theadjacent curved outer surfaces of parts 4 and conforms to and completesthe circle thereof at this point to provide an unbroken circular innerpole piece.

The flux carrying capacity of the plug 6 is sumciently small incomparison to the remaining pole piece area that its removal does notdisturb the permanent magnet strength by knockdown effect by reason ofits removal. Thus the pole face area provided by plug 6 is about six percent of the total effective pole face area of the inner core. Itspresence improves the air gap flux distribution but has negligibleeffect on its magnitude. The air gap arc length of plug 6 is about 15degrees. Also the air gap dimensions cannot be changed by reason ofremoval and insertion of the armature assembly. Hence the armature maybe removed for inspection, repair, and adjustment without changinginstrument calibration insofar as flux strength and air gap relationsare concerned. The opening at 26 and its use for the purpose describedeffectively utilize what would otherwise be idle space, as it is notneeded to carry magnetic flux. The resulting instrument is exceptionallyrugged and compact, using a small number of parts and only a fewfastening screws or bolts.

It is to be noted that the stationary support 21 for the lower spiral I8is positioned in line with the core opening 1 so that it too may passthrough such opening in the assembly and disassembly,

It is to be further noted that with the inner core parts 4 and 5 anintegral part of the permanent magnet structure and never removedtherefrom, no magnetic keeper or other precautions are necessary toprevent demagnetization of the permanent magnet after it has beenmagnetized. In other words, there can be no change in the reluctance ofthe magnetic circuit which would cause demagnetization because the partsof the magnetic circuit which determine mini- 4 mum reluctance arepermanently assembled and comprise an integral structure. Other parts ofthe instrument not particularly mentioned may conform to usual practice.

The permanent magnet may therefore be magnetized at a high flux densityand have a small knockdown corresponding to the reluctance of armatureair gap in the magnetic circuit when the plug 8 is removed. This permitsof exceptionally efllcient utilization of the permanent magneticmaterial and results in a rugged instrument of small size and highsensitivity.

The structure of Fig. 2 is polarized by employing a magnetizer with aninner C-shaped pole piece plug which fits within the inner periphery ofthe pole shoe 2 from one lateral side and is magnetically spaced fromthe inner core parts 4 and tongues 5 and an outer ring-shaped pole piecewhich embraces the outer periphery of the outer ring 3 from the otherlateral side. When the magnetizer is energized, the permanent magneticmaterial i is polarized in a radial direction. The desirable features ofa. permanently assembled one-piece field structure which is polarizedafter assembly, such as shown in Fig. 2, are not confined to thatparticular structure. For example,

the inner core and tongue may be in the form of a question mark asrepresented in Fig. 6.

In accordance with the provisions of the patent statutes we havedescribed the principle of'oper-' ation of our invention, together withthe apparatus which we now consider to represent the best embodimentthereof, but we desire to have it understood that the apparatus shown isonly illustrative and that the invention may be carried out by othermeans.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In an instrument,a permanent magnet flux path assembly comprising aninner circular tubular pole shoe of magnetic material, an outer circularyoke of magnetic material, an intermediate portion of permanent magneticmaterial extending between said pole shoe and yoke and polarizedradially, said inner and intermediate portions having an open sector andsaid outer portion having a symmetrically divided two-part tongueprojecting radially inwardly through such open sectors in symmetricallyspaced relation to the intermediate and inner portions and forming apair of similar sector shaped inner core parts spaced from said innercircular pole shoe by sector shaped gaps conforming to the same circle,said inner core parts being spaced apart a distance sufficient to passthe side of an armature coil therethrough, said permanent magnet fluxpath assembly being permanently assembled as an integral structure priorto polarization of the permanent magnet.

2. In an instrument, a permanent magnet flux path assembly comprising aC-shaped part and a ring shaped part embracing the outer periphery ofthe C-shaped part, a two-part inner core within the C-shaped part andjoined to the ring part by tongue extensions through the opening in theC-shaped part, the inner periphery of the C-shaped part and the outerperipheries of the core parts forming concentrically disposed pole facesseparated by a narrow concentric circular air gap of the order of 250degrees arc, said parts being made from magnetic material and includingpermanent magnet material polarized to produce flux across said air gapbetween the C-shaped part and the inner core parts, all of the air gaparc and occupying less than ten per cent of such arc.

3. An electrical measuring instrument comprising a magnetic circuitwhich is closed by magnetic material except for a circular air gapextending over an arc of between 180 and 300 degrees, said materialincluding a permanent magnet for producing flux across said gap. themagnetic inner core material forming the inner surface of said circulargap having an opening at the center of the circle conforming to the gap,a pivoted armature shaft extending through said opening, an armaturecoil carried by said shaft with one side adjacent the shaft within suchopening and the other side in the circular air gap, said magneticcircuit being a permamently assembled integral structure, except for asection of the inner core which is removable for the purpose ofthreading the armature on such core, said removable core section beinglocated at the center of the gap arc and having an air gap arc lengthnot exceeding degrees. 4; A field structure for an electrical measuring'instrument comprising an inner O-shaped pole piece of magnetic material,an outer circular magnetic yoke, an inner magnetic core within theC-shaped pole piece Joined to the yoke by magnetic tongue meanswhichenters within the c-shaped pole piece through the opening in the 0thereof and a c-shaped portion of permanent magnetic 'material betweenthe outer yoke and inner pole piece, said parts being permanently andintimately united into a one-piece assembly and the permanent magneticmaterial being polarized in a radial direction after such assembly,theinner core being spaced fromthe inner pole piece by an air gap, anarmature shaft opening within the inner core piece and an opening in theinner core piece for permitting an armature coil to be threaded thereonwith one side in the shaft opening and the other side in the air gap. a

5. A field structure for an electrical measuring instrument comprisingan inner C-shaped pole piece of magnetic material, an outer circularmagnetic yoke, a magnetic core within and spaced from the C-shaped polepiece, magnetic tongue means joining the core to the yoke and enteringthe c-shaped pole piece through the opening in the C thereof, and aC-shaped portion of permanent magnetic material between the C-shapedpole piece and the yoke, the inner core and yoke being divided into twosymmetrical sections leavshaped pole piece of magnetic material, acircular outer magnetic yoke. a magnetic core within and spaced from theinner O-shaped pole piece, magnetic tongue means securing the core tothe yoke, and tongue means entering the C-sh'aped pole piece through theopening in the 0 thereof, permanent magnet material of c-shape betweenthe inner C-shaped pole piece and outer yoke, the yoke, core and tongueportions being made of magnetic sintered oxide and all of said partsbeing permanently and intimately united by casting into an integralassembly, saidpermanent magnetic material being polarized in a radialdirection after such assembly.

7. An electrical measuring instrument comprising a magnetic fieldstructure comprising an outer circular magnetic yoke. a c-shapedpermanent magnet having an inner pole piece of like shape supportedwithin the yoke, an inner magnetic core forming a circular airgap withthe said inner pole piece, magnetic tongue means joining the inner corewith the outer yoke, said permanent magnet being radially polarized toproduce a flux across said air gap, the core and tongue I being dividedinto two symmetrical parts by an intervening opening, an armatureassembly frame having upper and lower bearing supports connected by ayoke, said yoke extending through the opening in said tongue, anarmature shaft supported by said frame centrally of the inner core, anarmature coil carried by said shaft and threading the core with one sideadjacent the shaft and the other side in said air gap, and a. magneticplug carried by said frame closing the opening in said core adjacent theair gap. said frame and the parts carried thereby being removable as aunit when the armature coil is turned into alignment with said plug.

8. An electrical measuring instrument comprising a magnetic fieldstructure comprising inner and outer concentric magnetic pole piecesforming a circular air gap of the order of 250 degrees arc, apermanently magnetized magnetic circuit Joining said pole pieces andincluding a tongue part extending radially from the inner ole piecebetween the extremities of the air gap arc. the inner pole piece havinga central axial opening which extends into the tongue part and aremovable plug part adjacent the air gap opposite to the tongue part, anarmature assembly frame having a yoke secured in the opening in saidtonguepart, a shaft pivoted in said frame and extending centrallythrough the axial opening in said inner pole piece, an armature coil onsaid shaft with one side adjacent the shaft and the other in said airgap and surrounding the intervening portion of the inner ole piece, theremovable plug of said inner pole piece being secured to said frame,said frame with the shaft, coil and plug parts carried thereby beingaxially removable as a unit when the coil is turned into alignment withsaid plug.

9. An electrical measuring instrument comprising magnetic circuitcomprising a O-shaped permanent magnet having a c-shaped inner polepiece, an outer circular magnetic yoke, an inner core within theC-shaped pole piece and forming therewith an air gap of the order of 250degrees arc, and; magnetic tongue Joining the core with the yoke throughthe opening in the C of the permanent magnet and its inner pole piece,the core and yoke being separated into .two symmetrical portions by anopening in line with the center of the tongue and core, all of saidmagnetic circuit parts being permanently and intimately united 7 into anintegral assembly as by cast welding, and the permanent magnet beingpolarized ina radial direction after such assembly, an armature assemblycomprising a framework of nonmagnetic material having upper and lowerbearing supports, a yoke connecting the two, a shaft pivoted in thebearing supports, a coil carried by the shaft, and a magnetic plugsupported from the yoke of the frame, the yoke of said frame beingdimensioned to fit into the opening in the tongue of said magneticcircuit with the armature shaft coinciding with the axis of the core andwith the magnetic plug closing the opening in the core, the plug beingsecured to the yoke of the frame by a support which curves around theshaft, the coil having one side adjacent the shaft and threading 8 thecore with its other side in the air gap, said armature assembly andparts carried thereby being axially removable as a unit when the coil isin alignment with the plug.

MYRON 8. WILSON. FRANCIS M. LEARNED.

REFEllENCES CITED The following references are of record in the 10 fileof this patent:

UNITED STATES PATENTS

